as Manish said it earlier it's not possible to restore the deleted images and the folder - unless you're having a backup of your database AND the "document_library" folder.

If you have such a backup you should import the db backup to a new database, then check which dlFolderId and dlFileEntryIds you have to restore (based on the accidentially deleted folder name). Export them to a sql file and import it in your production database. Next you have to copy the folder and all files in it with the appropriate id from the backup to your procuction server into the "document_library" folder.